The present invention generally relates to a one-piece flat-sided extrusion for use in multiple applications, such as heat exchanger headers or other high pressure vessels, and methods of making the same.
Extruded products are used in a variety of applications. A primary use of extruded products is to provide structural strength or stiffness to various structural shapes, such as beams, angles, channels, and tubing. In manufacturing steel extruded products or extruded products made out of heavy material, the material is heated and pressure is applied to force the material through a diehead. As the flow of material is forced through the diehead, the material tends to conform to the shape of the cutout or opening in the die, producing an extruded product with a cross-section that matches the shape of the opening in the die. As the extrudate exits the diehead, it is cooled (usually with water) to harden the extrudate into the shaped article intended from the process.
When an extruded product is being produced for use in a high pressure environment, strong materials, such as steel or a form of steel having additives intended to strengthen or provide other enhanced structural or physical properties, need to be used. For example, cogeneration facilities employing heat exchangers commonly have cylindrical header pipes made of steel. They are manufactured with round, heavy-walled steel tubing and must comply with American Society for Testing and Materials (ASTM) standards for high pressure vessels.
Heat exchangers in general are used in a variety of applications to heat or cool gases or liquids. Heat exchangers typically include two parallel header units with a plurality of tubes connected between the two headers. Such flow designs are referred to as parallel-flow, because the tubes are parallel to each other, but the process is in actuality more of a xe2x80x9ccross-flowxe2x80x9d pattern. Liquids or gases flow through the tubes (side-to-side or up and down), from one header to the other, and forced outside air runs perpendicular to the tubes, i.e., crossed with the liquid or gaseous flow. The headers act to collect the cooling or heating medium being used in the application and direct the medium through the tubes.
A variety of different header shapes have been used for different applications. For applications involving high pressure within a heat exchanger, such as in cogeneration facilities, the headers are typically extruded into a cylindrical shape. Cogeneration heat exchanger headers have also been formed having a rectangular shape, but these headers have joints where individual portions of the header are attached or welded together. Rectangular headers have also been criticized as not being as good pressure vessels as are cylinders.
FIG. 1 shows one cylindrical header pipe 10 of the type currently in use. Header 10 has tube receiving apertures 12 drilled at various angles to surface 14. Tubes 16 are inserted into apertures 12.
Cylindrical header pipes 10 with this structure present some problems due to their shape. The fabrication process is costly and difficult due to the odd angles at which apertures 12 need to be machined in the continuous curving surface 14 of the header 10 to allow for the incorporation of tubes 16 into the header 10. The apertures 12 are drilled on a contoured surface 14, commonly called hillside boring. In manufacturing apertures 12, deformation may occur around the edges of the apertures 12. Furthermore, structural integrity is jeopardized by the removal of material in a concentrated area 17, resulting in deformation caused by lack of structural support. The contact thickness of the area 17 where the header 10 and the tubes 16 are to be connected becomes less than the thickness of the remainder of the header 10 since the aperture 12 is formed on a curved surface 14 rather than a flat plane. As a result, the aperture 12 is angled. Accordingly, the coupling of the end of the tube 16 to the tube receiving aperture 12 of the header 10 becomes unstable.
For example, the welding process to attach tubes 16 is extremely difficult because of the contoured areas encountered with a curved connection surface 14. Thus, the junction between the header 10 and the tube 16 is rendered incomplete, causing leakage of the heat exchange medium.
Additionally, an unnecessary space 18 is formed around the tube 16 when it is inserted into the area 17 inside of the header 10 so that the flow efficiency of the heat exchange medium is lowered, and the necessary amount of charge of the heat exchange medium is increased. It is also difficult to adjust the depth to which the tube 16 is inserted into the header 10 during manufacturing.
Moreover, when tube receiving apertures 12 are manufactured in cylindrical headers 10, a second stage of machining is required to machine chamfers 13 around each aperture 12 drilled for the tubes 16 to accommodate the welding process. This second stage of machining is time consuming and adds additional cost to the production of the header 10.
An additional header is discussed in U.S. Pat. No. 5,246,066, which discloses an extruded tank that has four solid longitudinal side walls. Three of the walls are generally flat-sided and a fourth side, into which flat sided extruded tubes are inserted, is formed as an arc or a curvature bowing outwardly from the fluid-containing space. This curved shape also presents the above-discussed problems.
A one-piece header with a flat side is disclosed in U.S. Pat. No. 5,842,515. However, this header is not extruded to form one continuous piece, but is formed by bending a malleable aluminum sheet with both sides of the sheet coming into contact with each other to form a hollow passage inside the header, and then brazing the sides of the sheet together to seal the opening. This type of header would not be appropriate for use in a high pressure environment, as the thickness of steel required when using high pressures would not allow the manufacture of the header through bending.
An extruded aluminum header pipe with a flat side is disclosed in U.S. Pat. No. 5,622,220. Similar to other aluminum headers, this header would not be suitable for use in a high pressure environment. The header pipe has a D-shaped cross-section with a flat side and is manufactured by extrusion. This header, however, is manufactured for use in an automobile air conditioning system and accordingly, is made out of aluminum. Additionally, this header has a flat section with a rounded section extending from opposed sides of the flat section. A header for use in a cogeneration facility or other high pressure vessel needs side walls that are substantially perpendicular to the flat section and that provide more structural support and integrity than the minimal support provided by the rounded section defining the D-shaped header in U.S. Pat. No. 5,622,220.
Furthermore, there are distinct differences in the manufacturing requirements, and thus the components used, in an air-conditioning heat exchanger unit as opposed to a cogeneration facility heat exchanger unit. For example, the size of a cogeneration facility heat exchanger unit is several hundred times larger than an automobile (or other similar-type use) heat exchanger unit. Because of this, the construction materials used in a cogeneration facility heat exchanger are entirely different. The extreme pressures and temperatures reached during normal operation of a cogeneration facility would render the processes and materials used to manufacture an automobile (or other similar-type use) heat exchanger unit inadequate for use in cogeneration facilities. For example, the stresses accruing during operation of a cogeneration facility are greatly increased. Accordingly, the construction materials for a heat exchanger unit for use with a cogeneration facility must be able to withstand extreme pressures, for example, those up to 3600 psig. The thickness of the material used in a cogeneration facility heat exchanger is also increased from that of an automobile air conditioning (or other similar-type) heat exchanger due to the pressures involved.
Moreover, different manufacturing methods and material specifications are required for cogeneration facility heat exchanger units as opposed to automobile (or other similar-type use) heat exchanger units. For example, the criteria for attaching tubes to a header for use in a cogeneration facility must meet standards for high pressure vessels set forth by the ASTM for construction of heat recovery steam generators (HRSG""s).
It is also not possible to form tube receiving apertures in the thick steel by pressing, which is the method used in U.S. Pat. No. 5,622,220. In forming a heat exchanger for use in a cogeneration facility, apertures must be drilled in a header and tubes are secured by being welded into the apertures.
U.S. Pat. No. 5,622,220 also requires brazing metal plates made out of thin aluminum to facilitate the connection of the tubes to the header pipes. The patent does not disclose a heat exchanger for use in a cogeneration facility, nor does it disclose a steel header or steel extruded product, or any way of forming a header suitable for use in a cogeneration facility.
Thus, it is desirable to form a steel header through one extruded piece that is suitable for use in a cogeneration facility and that has a flat bottom portion wherein tubes can be easily attached and flat sides to provide support and structural integrity.
The present invention provides a one-piece extrusion having a flat bottom portion and supporting flat sides. The one-piece extrusion is particularly appropriate for use as a heat exchanger header on a cogeneration facility. This invention reduces the number of components forming the header to one continuous piece that is manufactured out of steel or a steel alloy. This invention provides a header that eliminates the need for the complicated manufacturing and welding procedures encountered with the cylindrical headers currently being used. It eliminates the need to drill tube receiving apertures on a contoured surface and provides a way to manufacture the apertures and form the chamfers on the edges of the apertures substantially simultaneously. This invention also provides a seamless header having a flat bottom portion and supporting flat sides that is not formed by bending or creating seams, but is instead one continuous header without joints or seams.
The flat bottom portion of the header of the present invention facilitates the attachment of tubes to the header by permitting the openings for the tubes to be machined more easily. The machining and welding can be done on a flat surface, which eliminates the need for specially angled entry points for the attachment of tubes or for welding on an angle, which often causes leaks. This is of particular concern when manufacturing a heat exchanger header for use in a cogeneration facility, as opposed to a header used in an automobile air conditioning heat exchanger unit or other uses that are not subject to a high pressure and temperature atmosphere. Steel cogeneration facility headers are required to be pressure-certified according to ASTM standards, providing additional difficulty and obstacles when manufacturing headers for such uses.
The strong steel header of the present invention allows the tubes to enter the flat bottom portion of the header at a substantially perpendicular angle to the flat bottom portion, providing an easier, stronger and faster overall weld due to the ease of access all around the entry points of the tubes into the header.
This substantially perpendicular entrance of the tubes decreases the number of potential leaking joints. It also causes less material to be lost in the machining process. The material typically lost in the machining process of cylindrical headers is shown in FIG. 1, where the thickness of header 10 at area 17 is less than the thickness of the remainder of the header 10. The flat bottom portion of the present invention allows for a more conventional drilling method, which strengthens the structural integrity of header by causing less material to be lost, and is less time consuming and less costly.
The present invention also provides more surface area than the cylindrical headers presently used because it has a flat bottom portion, allowing more tubes to be attached to the header because tubes can be placed right up to the edge of the flat bottom portion if desired or necessary. The invention also allows the tubes to be attached more efficiently by providing a flat surface for drilling and welding the tubes to the header. Furthermore, the flat bottom portion of this invention also allows a chamfering tool to be mounted to the external portion of the drill or boring tool in order to chamfer the edges of the apertures while the apertures are being formed, rather than requiring the separate chamfering step that is used to manufacture cylindrical headers.
The present invention also provides a header having two flat sides formed integrally with and adjoining the flat bottom portion of the header. The flat sides help provide the structural support and integrity necessary to stabilize and strengthen a header for use in a cogeneration facility heat exchanger. The flat sides also allow a greater number of headers to be placed closer together, without taking up the space required for cylindrical headers.